I drive and monitor the cooling system in my 1999 base Deville as if it ALREADY has a blown headgasket from the stripped head bolt issue. The year and the mileage makes it a sitting duck for that issue at 110k.

I run the green Peak any make and model antifreeze and just put 5 Delco seal tabs in the upper rad hose. It drives the normal operating temp 197-213 on the highway but if you really push it up mountains with the a/c on the temp will climb as high as 235 according to the digital readout on the base Deville cluster. This is driving it as if I WANT it to warm up and not taking any precautions like turning off the a/c or driving slow on STEEP inclines after driving the car at least 10 miles to know its fully warmed up.

In the 1200 or so miles I have driven the car I monitored everything close. Sure enough, I was loosing coolant and achieved 255 degrees last week but was very relieved to find it was the lower coolant pipe leaking near the pulleys. I just assumed it was where the coolant tank boiled over and this issue went unnoticed a few weeks. A good friend of mine had the part in stock and the two of us changed it with the engine still mounted in the car. It wasnt fun, but possible.

I plan to have the timsert job done WHEN the gaksets go but no sense in doing it any sooner than needed. I think I can even drive with the cap loose and get even more miles if needed.

I dont take the car on long trips but go 30-40 miles from home with it and see no signs of a typical head gasket issue. Things like white smoke, hard starting, or oil and coolant mixing are not happening.

I have found that filling the reservoir to the top will cause some to boil out and a few bubbles occur in the tank at idle with the cap off. These are the few things that lead me to believe I am in the early stages.

Sorry that a lot of this was discussed in other posts but I wanted to get an idea on the 235 thing and driving this car with cap loose. It SEEMS like the exhaust in the coolant leak would help pressurize the system enough to keep it cool. I asked a guy at the Cadillac dealer and he agreed.

Ranger

07-27-09, 10:18 PM

DO NOT EVER drive it with the cap loose. That will lower the boiling point and will certainly cause a boil over. I can't believe anyone at the dealer would agree with that. Who did you talk to, the janitor?

I agree, some of you symptoms sound like early stages. Others sound normal. If it is a head gasket, it will let you know soon enough.

DO NOT E
Might want to consider seeing Jake. http://www.northstarperformance.comNot too far from you at all and the best deal on saving the POS you have there. :histeric:

DanDeville99

07-28-09, 01:01 AM

DO NOT EVER drive it with the cap loose. That will lower the boiling point and will certainly cause a boil over. I can't believe anyone at the dealer would agree with that. Who did you talk to, the janitor?

I agree, some of you symptoms sound like early stages. Others sound normal. If it is a head gasket, it will let you know soon enough.

I agree with you, especially on a normal engine. I just assumed that the exhaust gasses getting into the coolant, IF that is the case, would help raise that boiling point back up. The car is driven in Upstate NY where it does not get too hot. I was standing at the parts counter at the Cadillac dealer and the parts guy asked a tech who walked in for a part. That is the best time to catch these guys when its informal.

Thanks to the link to the site. I am going to try the test he mentioned. It may save miles of driving and a lot of gas.

DanDeville99

07-28-09, 11:53 AM

Ok, I am a little more convinced that exhaust is getting into the coolant on this car. First thing cold this morning BEFORE STARTING I removed the cap and heard SOME pressure release. After 14 hours there should of been NONE? I had a feeling the car may still pass the test mentioned at northstarperformance so I took it to another level. I installed only a 7 lb cap on the car and hooked up a beverage bottle to the drain hose on the black tank. When I did the test about 3 times of getting up to 70 a few times, slowing down to 30 the car would not go past 228 degrees on an 82 degree day with the a/c on.

Of course when I got home and opened the hood the beverage bottle was full of purged coolant but the car was not boiling. Before I leave again I will have to dump it back in and replace the 15 psi cap.

I am thinking about making a minor modification that may allow even longer use of this car before the engine is torn down. Has anyone ever tried to connect the purge hose (the one that dumps on the ground when the cap lets off excess pressure) into a conventional NON-Pressurized overflow jug like older cars had? Then I could run the lower p.s.i cap, and increase my coolant capacity. Right now there is a fine line in the sand as to how high I can fill my black OEM tank. IF I exceed that, it just gets sprayed back out eventually. This way the excess goes into the extra jug, then when the car cools it MAY get drawn back in. IT all depends on the pressures but I think I could run the 7 psi stant lever lock cap if I had a place to recover the lost coolant.

Again, if the HG's are blown, they are blown but I dont see the need to repair them yet if the car still gets me from point A to point B with a little bit of running on the warm side. The second I see white smoke or coolant in the oil, it gets parked to avoid bottom end destruction. I came into this car KNOWING it was a prime target for HG's. It sat around over the last few years and was driven very little with old Dex-cool still in it.

By ANY freak chance has anyone ever discovered the cap to be bad? My other GM car that is also famous for HG trouble is a 3.4 venture van. I thought for sure it was done a year ago but it turned out to be just the cap. The system would build up extreme pressure and peg the gauge.

Submariner409

07-28-09, 12:24 PM

If you are filling the surge tank over half full, COLD, it is way overfilled and will blow off coolant with every warmup. That airspace is there specifically to allow the entire coolant/system to expand and contract with temperature changes. Full to the top and it's no wonder the cap leaks. Coolant blows off, pressure drops and the coolant boils.

Put the 18 pound cap back on and leave it there !!! It's no wonder you're having problems - the cooling system IS NOT designed to run at less than 16 psi. Yes there will be some pressure in the system after overnight, and if there is, the head gasket is not blown. Restore the cooling system to design normal and stop trying to outguess the engineers.

The purge line is SUPPOSED to constantly bleed coolant back to the surge tank: That tank is also connected to the system at the bottom, and the purge line removes air and gasses from the coolant in order to prevent pump cavitation. Stick the purge line somewhere else and you pump all the coolant out !!!

The coolant overflow line is dumping coolant because the system is grossly overfilled !!!

DanDeville99

07-28-09, 12:41 PM

If you are filling the surge tank over half full, COLD, it is way overfilled and will blow off coolant with every warmup. That airspace is there specifically to allow the entire coolant/system to expand and contract with temperature changes. Full to the top and it's no wonder the cap leaks. Coolant blows off, pressure drops and the coolant boils.

Put the 18 pound cap back on and leave it there !!! It's no wonder you're having problems - the cooling system IS NOT designed to run at less than 16 psi. Yes there will be some pressure in the system after overnight, and if there is, the head gasket is not blown. Restore the cooling system to design normal and stop trying to outguess the engineers.

Thanks so much Sub. I think you just saved me hours of grief and a lot of money. The whole problem started with the coolant pipe leak. Then even after it was fixed I would check that black tank every few days and feel the need to have it 3/4 full instead of 1/2. From there the chain of events would compound just as you described.

My OEM cap says 15psi "add dex-cool only" Therefore its obviously a GM cap. LOL. Should I buy a 16 or 18 and go with the stant lever lock type? I am sure there is a thread on caps if I search for it either way.

DanDeville99

07-28-09, 12:59 PM

"The purge line is SUPPOSED to constantly bleed coolant back to the surge tank: That tank is also connected to the system at the bottom, and the purge line removes air and gasses from the coolant in order to prevent pump cavitation. Stick the purge line somewhere else and you pump all the coolant out !!!"

Just wanted to clarify that I may of been confusing when I was talking about lines at the black tank. I left the actual purge line that runs along the intake to the black tank (across engine) alone. I get some crazy ideas at times but messing with that would be asking for trouble, HA! The only line I tampered with was the one that would normally be aimed at the ground near the pulleys. Car was allowed to idle about 30 minutes with the 7 psi cap on and the correct amount of coolant. I wanted it to blow off any excess while still at home. Fans cycled in conjunction with A/c and car stayed around 203 tops. VERY HAPPY. Now everything is back to "normal" with the GM 15 psi cap and I am off for a 60 mile local trip! Thanks again Sub, you really saved me a lot of future headaches. Sometimes I OVER THINK and I will admit I never totally understood coolant pressure and boiling points. Wish I had posted on a forum back when I fought with a GM 5.7 Diesel HG a few years ago doing similar stupid things! HA!

Submariner409

07-28-09, 04:16 PM

Leave the GM stock 15 psi cap on there. Whatever type it is: all these tanks are as different as fish in the sea - mine has a screw on cap set to 18 psi. Others are screw on at 15 or 16 psi. Others are twist-to-lock at 15 psi.

Use your stock cap or replace it with an identical unit from NAPA.

Ranger

07-28-09, 05:09 PM

I will admit I never totally understood coolant pressure and boiling points.
Very simply put, water boils at 212 at sea level pressure (29.92). Raise the pressure and the boiling temperature rises. Lower it, and it goes down. That is why you pull a vacuum (the opposite of pressure) on the A/C system before charging it. You can actually boil off any moisture in the system at 70 degrees.

DanDeville99

07-28-09, 09:48 PM

What a day I had! I dont know what to think now. The car acted perfect for around 45 miles of city and highway driving today. Before seeing the post about leaving my 15 psi cap I stopped at Advance auto and asked them to look up the cap for my car. They came up with 16 and I opted for the Stant lever lock.

When I opened the hood to change it I noted about 12 ounces of coolant was in my gatorade bottle I keep by the battery. Instead of going in the ground I like to catch the excess coolant plus monitor it. I just assumed I never had the correct level in the tank, I think it has to be actually COLD to know you have it at half based on much appreciated advice I received earlier today.

ANyway, i installed that cap and 12 or so miles later of city, then highway, then a BIG hill I got all the warnings. A/c off, Idle engine...then STOP. I immediately did of course and let it cool awhile. I KNOW this is dangerous but I was able to get enough pressure released to get the cap off while it was still in the 230's. I started it back up and filled it again with mostly water. At this point I just wanted to get it home and deal with it the next day totally cold. Well, going back down that big hill it shot right back up to the 250's again. I stopped at some relatives house and let it cool at least half and hour and filled it again and it pegged in only minutes, once again.

I began another cool down, fill up but this time it wasnt going to cool down. It went from 229 to IDLE ENGINE just like that. SOmething told me check the T*stat but when I got the bottom hose off (still hot while engine ran and I was spraying water on my hand) coolant did come out. Then with engine running I had a helper spraying water in tank while I undid top hose. After a pause water came out there and to make a long story short, the car dropped down immediately and ran home on mostly water at 197 as usual.

My grandpa keeps saying take back the new T*stat for an exchange and then drive the rest of the summer without one at all. I just dont think this car would appreciate that. If I buy the stud bolt kit and tear this down I will be so mad at myself if I find there was no problem. Anyone who doesnt know N*star says noway that car has blown a HG but we all know better, hA!

The car is worthless the way it is (black base 99 deville with 110k) and I know if it was fixed right it would be a great car with many more years left in it. So frustrated right now. Thinking about just yanking the plates before I make things any worse, LOL.

Ranger

07-28-09, 10:00 PM

That does not sound good. Get the block test kit from Napa and test the coolant for the presence of exhaust gases. And DO NOT heed gramp's advice, no mater how well intended. You NEVER drive a car without a radiator cap. You won't be any better off than you are now and won't get more than a few miles.

97EldoCoupe

07-28-09, 10:14 PM

If I buy the stud bolt kit and tear this down I will be so mad at myself if I find there was no problem.

Unless you find a brand new set of head gaskets in there and perfect threads in the block, you won't be mad at yourself.

Do a leakdown test on the cooling system. Pressurize the whole system to 15 PSI and see if the pressure drops off. If it holds it, you're good. If it loses it, well, time to find the leak. All it takes is a pinhole leak somewhere, enough to let some pressure escape, to lower the boiling point of the coolant mix.

235 degrees is the highest you will ever want to see a Northstar go. Give it 240 for sensor variance. Any higher then something's screwed.

I know everyone looks at the Northstar HG job like "holy crap this looks like a big messy job". The good news is, it's not as bad as you think. Change the head gaskets and install studs and your problems will get much smaller. Any cooling system problems after that are easy to take care of (rad, water pump, t-stat, hoses, heater core, etc.).

I see it this way: If nothing small seems to be causing the trouble, before replacing what doesn't seem necessary, get the HG's done. At very worst, you have gotten some important preventative maintenance done and over with.

I have a customer from Toronto who's stuck in Boston, MA right now with his Caddy. There's a shop in Boston who'll be installing the studs because he can't make it home- HG's blew on his vacation.

Better and cheaper to get it done before you go on a long trip. This saves headaches, towing charges, and possibly not finding anyone on short notice to do the job.

If you decide not to get them done right aways, I wish you the best, hopefully it's just a small issue that has been overlooked, but from what you're telling us, I'd be leaning toward the HGs. One good overheating on an old Northstar will pull the bolts that were holding by a thread.

97EldoCoupe

07-28-09, 10:18 PM

Ranger is absolutely right. Some of my customers have done this too- but running without the cap tight will cause boilover pre-maturely. You'll lose your coolant and there won't be anything left to cool the engine.

Mark C

07-28-09, 10:41 PM

Heres something a guy in my town did on his Deville when the HG started to go. He got a house hot water radiator vent can. Its a brass can about the size of a medicine bottle with a 1/8" NPT fitting on one end and a vent cap on the other, there is a float inside it that is designed to purge air from your baseboard radiators in your house He put that on a "T" fitting with two hose barbs and installed it in the purge line near the water pump fitting. You need to tie wrap it to something so it stays vertical, and it should also be mounted up high, about even with the top of you throttle body so its the high point in the system. It will collect all the "air" coming thru the purge line and vent it off without carrying any of the coolant with it. He figured it would get his car thru another couple of months so he could find a new car to drive, but after he did that he never had another problem with the car for another year. It won't cure a huge HG problem but might help in situation where the HG is just starting to go, and it only costs about 20 bucks for all the peice you need to make it work.

Destroyer

07-28-09, 10:49 PM

The car is worthless the way it is (black base 99 deville with 110k) and I know if it was fixed right it would be a great car with many more years left in it. So frustrated right now. Thinking about just yanking the plates before I make things any worse, LOL.
It's pretty worthless even after you dump $3-$4k fixing it. Get rid of it and move on. This isn't the only problem area with these cars. :helpless:

DanDeville99

07-28-09, 11:37 PM

That does not sound good. Get the block test kit from Napa and test the coolant for the presence of exhaust gases. And DO NOT heed gramp's advice, no mater how well intended. You NEVER drive a car without a radiator cap. You won't be any better off than you are now and won't get more than a few miles.

Hi sorry again for the confusion. I am new to the whole forum thing. T*stat was supposed to be thermostat. I put a new one in around a month ago when I did the bottom hose and got rid of the dex-cool. Today the car acted exactly like a stuck thermostat. Obviously, due to the gasket provisions, the thermostat would have to be busted up and still installed causing a partial restriction to the coolant flow. I still dont think its a good idea either way. On cooler days the car would run too cool, especially on the shorter trips the car will mainly be used for until fixed right.

DanDeville99

07-28-09, 11:54 PM

It's pretty worthless even after you dump $3-$4k fixing it. Get rid of it and move on. This isn't the only problem area with these cars. :helpless:

WOW, are people really willing to pay THAT MUCH to fix these? The guy on this forum who fixes the problem once and for all and willing to stand behind the repair only charges 2200? I planned to be between 700 and 1500 depending on if I did MOST of the work myself or have a friend who is very experienced with timeserts do it. He has a used auto lot and full service shop and he specializes in luxury cars. I am sure I could convince him to do the stud kit instead. HA!

If all said and done I had 3500 in this car with SOME of the common problems already addressed, (new air ride, coolant pipes and the rear spindle repair) I am not hurting too bad. Older family members are already eying it up and I know it would have years of great service left. I have many of the common spare parts for it already including the trans, radiator, body parts, etc. Pretty much at the point of no return already. I went this far, cant stop now!

DanDeville99

07-29-09, 12:14 AM

Heres something a guy in my town did on his Deville when the HG started to go. He got a house hot water radiator vent can. Its a brass can about the size of a medicine bottle with a 1/8" NPT fitting on one end and a vent cap on the other, there is a float inside it that is designed to purge air from your baseboard radiators in your house He put that on a "T" fitting with two hose barbs and installed it in the purge line near the water pump fitting. You need to tie wrap it to something so it stays vertical, and it should also be mounted up high, about even with the top of you throttle body so its the high point in the system. It will collect all the "air" coming thru the purge line and vent it off without carrying any of the coolant with it. He figured it would get his car thru another couple of months so he could find a new car to drive, but after he did that he never had another problem with the car for another year. It won't cure a huge HG problem but might help in situation where the HG is just starting to go, and it only costs about 20 bucks for all the peice you need to make it work.

MARC, I LOVE IT! LOL This is HOW I THINK. I kept my 1983 Buick Park Ave Diesel going with a blown HG a whole summer doing things like this. I even experimented trying to get the heater working again, HA. The diesels air lock the heater core but I dont think the Caddy N*star does. At this point I have little to loose and even have a spare engine from a previous 99 Deville. I really an eager to learn all I can about these engines.

mikelawson

07-31-09, 10:15 PM

If you ship the engine to me, I can repair it using Norm's inserts for 1300. That includes everything except shipping. If I towed the car or had it towed, I could do it for you for around 2000. Let me know if you have any other questions.

Mike

DanDeville99

08-01-09, 11:02 AM

Thanks Mike,

The car and I had a horrible day yesterday and I am still not convinced its a head gasket and either are 3 mechanics who saw the car when I stopped by for a cool off.

The car still passes the test at Northstarperformance.com. I got lazy and left the water to coolant ratio with way too much water after the last episode and forgot to take the one steep hill that makes the temp climb, at a slower speed at least. Sure enough, I got things boiling and messed up all the sensors. From there every few miles it was up to 255 - 260 yet I could have the cap off in no time without much trouble. Finally I got where I had to be after several additions of straight coolant.

After sitting nearly 3 hours the car was cooled and did not take much coolant to top it off. In under a mile it climbed all the way to 235 and said CHECK COOLANT. Same problems I was having adding coolant to the hot engine. (running of course) I pulled into a store and tore off the air box and grabbed the bottom hose. Sure enough, it was ice cold. In frustration I revved the engine by hand while holding the hose. Finally the hose warmed up, and the cars temp dropped down to 197. IT let me add another 1/2 gallon of coolant and 60 miles later, no matter how steep the hill or how fast I go up it, the car will not heat up past normal.

Now I am leaning towards a partially plugged radiator or a screwy thermostat. Wherever the engine temp sensors are I dont think they were getting any coolant yesterday when all this overheating started. If I do tear the engine out of this car, it was going to be a winter project. I know I will hear some strong opposition to this, but I am thinking about just busting up the thermostat and putting it back in as a big washer. Since the car only calls for a 180 degree anyway, it shouldnt be that hard to maintain that in the summer without a functioning thermostat.

Submariner409

08-01-09, 01:12 PM

The thermostat for a 1999 Deville begins opening at 188 and is fully open at 206. Your car should normally run at 193 - 198, or 50% -70% of thermostat opening.

The ECT sensor is down behind and below the throttlebody. PITA.

abs

08-01-09, 02:17 PM

Hi Dan-

Nobody likes to waste money, but why not throw in a brand new thermostat? I think they can be had for $20-30 and I'd recommend checking for them on RockAuto. Also, once you are there, you might consider replacing your water pump - I think this is about a $60 part. I've read of some folks who had overheating problems, but no hard evidence of a bad head gasket, who completed these steps and it resolved the overheating issues for them. Of particular interest, if the coolant had not been properly maintained before you got the car it is completely possible that the coolant became acidic and damaged either the pump or the thermostat. If it were me, I would consider doing that first since a general rule of thumb when making repairs when a conclusive diagnosis is not possible is to start with the most obvious/lowest cost alternatives first. In the event it is the head gaskets, and you repair them, then you can rest easy knowing you have a good pump and thermostat in the engine.

One other comment - if your lower hose is cold when the engine is overheating, that sounds like a bad/closed thermostat to me. Is it possible you installed the new thermostat improperly or may have installed the wrong part? I think these thermostats install with the bulb end toward the engine (Submariner or Ranger will correct me if I'm wrong).

Andrew

Ranger

08-01-09, 03:22 PM

If the lower hose was cold, you are not flowing coolant. Check the purge line and recheck the stat. I forget which way it goes in. I have never had to replace one yet, but I think ABS is correct.

Submariner409

08-01-09, 06:37 PM

Here ya go.............

DanDeville99

08-01-09, 07:03 PM

THanks guys, Yes, the stat goes in bulb end first, I installed it that way about a month ago. I headed out this morning for that same 60 mile round trip. At the end of the driveway it flickered low coolant. It took about a quart to get it back up to the half mark on the black jug. The car ran flawless MOST of the 86 degree day until on the way home I hit that same hill. This time I was on the interstate route for the hill and left the cruise on 71 and a/c on max. Ha, sure enough halfway up I achieved 230 so I shut off the a/c. By the time I was at the top I was at 250 so i got off the exit. Immediately the temp started going back down so I did not pull over and fuss with it. By the time I was back down the other side of the hill everything was normal. I have lost a quart of coolant in my makeshift auxillary recovery and monitoring system. HA! THe low coolant light did come back on but I ignored it knowing how little i really lost. Seems the car ran slightly cooler with that message on. Maybe it was a coincidence.

I did something today that many of you will not agree with. I went to a junkyard and looked around for a low pressure coolant recovery tank that would squeeze in by my battery up against the wishbone motor mount. HA, 1996 Geo Prism was slim enough. Also it has the two hoses connected to the low pressure snap on cap. Same way the older RWD Cadillacs did it. WHen the add on tank fills up, then the excess can drain on ground via the second hose. Whats ideal about this is I can see bubbles and know if I lost as much as a drop out of the OEM black tank. UNtil the car is fixed right I can open the hood in the morning and anything found in the "Geo" overfill tank can be dumped back in the black factory tank.

Another friend who owns a shop saw my hood up and stopped in and also says I need a radiator most likely. Grandpa sawed off my old thermostat and says to run that in the car for now until its fixed so I dont keep hitting 250 any more often then needed. I swear, if it was colder weather here there car would act totally normal. My goal now is to see how long I can drive it before the inevitable big repair comes. Maybe I can get lucky and someone steals it or rear ends it in the meantime HAHAH!

When the HG went on my last 99 Deville it was hard to start cold and you could not drive it more than 10 miles. Plus it smoked and the exhaust was ful of coolant. That time I opted for a used engine. Not on this car, the bottom end is too good and never had coolant in it YET!

DanDeville99

08-01-09, 08:08 PM

Guys, is the angle of my bottom hose bent too sharply? The engine is cool now and all pressure has been released. (138 degrees) Feeling with my hand this hose is about 50% restricted. Obviously pressure must force coolant through. I bought this hose about a month ago from advance auto parts and installed it myself. It LOOKS as if I shortened it some at the water pump the angle would not be as severe? Any thoughts are appreciated!

Ranger

08-01-09, 09:20 PM

Can't hurt to try. That bend looks a little tight, but not that bad.

Destroyer

08-01-09, 11:01 PM

Heres something a guy in my town did on his Deville when the HG started to go. He got a house hot water radiator vent can. Its a brass can about the size of a medicine bottle with a 1/8" NPT fitting on one end and a vent cap on the other, there is a float inside it that is designed to purge air from your baseboard radiators in your house He put that on a "T" fitting with two hose barbs and installed it in the purge line near the water pump fitting. You need to tie wrap it to something so it stays vertical, and it should also be mounted up high, about even with the top of you throttle body so its the high point in the system. It will collect all the "air" coming thru the purge line and vent it off without carrying any of the coolant with it. Does this fit under the hood or would a cowl induction hood be necessary? Where were you with this info when my N* let me down?

Mark C

08-02-09, 09:24 AM

Yes it will fit under your hood, they are about 4" by 2", and all you need to do is get the top of it higher than the top of the surge tank, so strapped to the side of the thottle body, the EGR tube or one of the brackets in that area would be fine. Heres a picture of one.

http://www.maid-o-mist.com/images/autoair2.jpg

Might not work for everyone, but it worked for a guy in my town. as it allows for purging of the gases without the associated loss of coolant, assuming you can collect the gas faster than it will build up pressure in the system that inturn opens the radiator cap.